The present invention relates to a discharge device driving method, and more particularly, to a method for improving the discharge process in a discharge device such as a plasma display panel.
A discharge device, which is driven by a pulse voltage, has at least one pair of electrodes and performs a discharge by applying the pulse voltage to at least one electrode. Examples of such discharge devices are a fluorescent lamp, a gas laser generator, a sulfur dioxide-removing O3 generator, and a plasma display panel. Here we will focus on the discharge device of the plasm display panel.
There are generally two types of displayxe2x80x94AC and DC. The DC plasma display panel uses electrodes exposed to a discharge space so that charges move directly between electrodes facing each other. On the other hand, in the AC plasma display panel, at least one of electrodes that face each other is surrounded by a dielectric, thereby preventing direct movement of charges between the electrodes. That is, as shown in FIG. 1A, the DC plasma display panel has a scanning electrode 2 formed on a frontal glass substrate 1 and an address electrode 5 formed on a rear glass substrate 6, which are directly exposed to a discharge space 4 so that a charge can move directly between the electrodes. The AC plasma display panel, as shown in FIG. 1B, has a scanning electrode 2 and a common electrode 3 which are covered by a dielectric layer 7, thus preventing direct charge movement between pairs of facing electrodes, that is, between the scanning electrode 2 and the address electrode 5 or between the scanning electrode 2 and the common electrode 3.
There are two methods for driving the plasma display panels as constituted above, that is, DC and AC driving methods whose classification depends on whether the polarity of a voltage applied for discharge sustainment varies with time or not. Both DC and AC driving methods can be applied to the DC plasma display panel, while only the AC driving method is available for the AC plasma display panel.
FIG. 1A illustrates a DC plasma display panel adopting a facing discharge structure, and FIG. 1B illustrates an AC plasma display panel adopting a surface discharge structure. As shown, the discharge space 4 is formed between the facing surfaces of the frontal glass substrate 1 and the rear glass substrate 6. In the DC plasma display panel, the flow of electrons supplied from the address electrode 5 (i.e., cathode) is the main energy source for sustaining discharge since the scanning electrode 2 (i.e., anode) and the address electrode 5 are directly exposed to the discharge space 4. In the AC plasma display panel, the scanning electrode 2 and the common electrode 3 are situated within the dielectric layer 7, thus being electrically isolated from the discharge space. In this case, discharge is sustained by the well-known wall charge effects. An example of the AC plasma display panel adopting the surface discharge structure is disclosed in the U.S. Pat. No. 4,833,463 by ATandT.
Depending on the constitution of electrodes for discharge, the plasma display panels are grouped into a facing discharge structure or a surface discharge structure. These structures, in turn, are divided into a two-electrode structure, a three-electrode structure, and so on to facilitate discharge. FIG. 2A illustrates a facing discharge structure, and FIG. 2B illustrates a surface discharge structure. In the facing discharge structure, address discharge for selecting a pixel and a sustainment discharge for sustaining discharge in a discharge space formed by blockheads 8 occur between the scanning electrode 2 and the address electrode 5. In the surface discharge structure, address discharge for selecting a pixel occurs between the address electrode 5 and the scanning electrode 2 which are orthogonal and face each other in the discharge space formed by the blockheads 8, and the sustainment discharge for sustaining discharge occurs between the scanning electrode 2 and the common electrode 3. The blockheads 8 act to form the discharge space and prevent crosstalk to adjacent pixels by blocking light generated during discharge.
For reliable operation of the plasma display panel as a color picture display, gray-scaling should be performed. Currently, a single field is divided into a plurality of sub-fields for time-share driving. FIG. 3 is a diagram for explaining a gray-scaling method for an AC plasma display panel applied to products, which is well-known to those skilled in the art. In the gray scale displaying method for the AC plasma display panel, a single field is divided into four sub-fields for time-share driving. Here, each sub-field has an address period 9 and a discharge sustaining period 10, and 24(=16) gray scales can be displayed with these four sub-fields. That is, since the ratio of the discharge sustaining periods in a first through a fourth field is 1:2:4:8, sixteen gray scales can be attained by constituting the discharge sustaining periods as 0, 1(1T), 2(2T), 3(1T+2T), 4(4T), 5(1T+4T), 6(2T+4T), 7(1T+2T+4T), 8(8T), 9(1T+8T), 10(2T+8T), 11(3T+8T), 12(4T+8T), 13(1T+4T+8T), 14(2T+4T+8T), or 15(1T+2T+4T+8T). For example, to display a gray scale of 6 at an arbitrary pixel, only the second sub-field (2T) and the third sub-field (4T) are addressed, and to display a gray scale of 5, the first and fourth sub-fields should be addressed.
FIG. 4 shows the waveforms of signals applied to a generally used AC plasma display panel driving method, showing the timings of signals applied to an address electrode 11, a scanning electrode 12, and a common electrode 13, respectively. In an erase period 14, to -accurately display a gray scale, the operation of the next sub-field is activated by generating a weak discharge and thus a wall charge caused by the previous discharge is erased. During an address period 15, discharge occurs only in a selected area, i.e., a pixel of the whole screen in the plasma display panel by selective discharge by means of a write pulse 17 between the address electrode 5 and the scanning electrode 2 which are orthogonal to each other. That is, image information converted into an electrical signal triggers each discharge of the addressed pixels. In a discharge sustaining period 16, the image information is realized by sustaining the triggered discharge on a pixel, which is addressed on a real screen, by means of successive discharge sustaining pulses 18.
In the plasma display panel driven by the above signals, it is well-known and empirically proven that luminescent efficiency increases using shorter pulses as the discharge sustaining voltage during a discharge sustaining period when driving the plasma display panel. This is because if a narrow pulse is used as the voltage applied during the discharge sustaining period, thermal and electrical loss is reduced and thus luminescent efficiency is increased.
FIG. 5 is a diagram explaining the discharge principle of an AC plasma display panel. Here, when the discharge sustaining pulse 18 having the discharge starting voltage 20 is applied, the wall charge 24 increases and thus the discharge voltage 25 drops. In the case of a normal discharge, discharge continues until a discharge extinguishing voltage 21 is reached, thus functioning to generate sufficient wall charge and controlling the distributions of wall and space charge densities to be favorable for the next discharge. However, as the discharge sustaining pulse 18 becomes narrower, a wall charge forming period 22 becomes very short. Thus; it is difficult to generate sufficient wall charge, and worse, a space charge controlling period 23 is absent; resulting in a complete loss of control of the wall and space charges after discharge is extinguished. In this case, to continue the discharge, the discharge starting voltage 20 should be very high, which makes adjacent electrodes susceptible to discharge. Therefore, the operating margin gets smaller and it is very difficult to discharge only the addressed pixel. That is, the margin for a pulse voltage for sustaining a stable discharge becomes smaller, and is lost in the worst case. According to the U.S. Pat. No. 4,833,463 of ATandT, a negative pulse (xe2x88x92VTC) is applied after an address electrode driving signal (address pulse, +VW/2) during an addressing period in order to reduce the discharge starting voltage. This is for forming the wall charge near a scanning electrode as much as possible by applying the negative pulse (xe2x88x92VTC) after the address pulse (+VW/2) and pushing out the wall charge formed near an address electrode by the apply of the address pulse toward the scanning electrode (discharge sustaining electrode or common electrode), thereby making easy the starting of the sustaining discharge. When the negative pulse is applied to the address electrode during the addressing period as described above, the wall charge which is sufficient for the sustaining discharge can be formed near the scanning electrode even if the voltage of the address pulse applied to the address electrode is low, thereby providing an effect of lowering the voltage of the address pulse. However, since the negative voltage is applied once only during the address period, there is no method for collecting the space charges formed in a discharge space during the sustaining period. That is, the voltage of the discharge sustaining pulse applied to the scanning electrodes cannot be lowered.
There are many improvements to be made in the discharge structure and driving method of the plasma display panel. In particular, the driving voltage is higher than those of other displays due to low luminescent efficiency and discharge-dependence. Accordingly, when the driving voltage drops during driving, reliable performance of the plasma display panel cannot be expected. Furthermore, another problem arises in that the visibility of moving pictures is lowered when time share gray-scaling is displayed.
To overcome the above problems, the object of the present invention is to provide a discharge device driving method in which the operating margin is increased to reduce the driving voltage as a driving characteristic and, particularly, the prevention of a decrease of the operating margin caused by driving a plasma display panel by a narrow pulse.
To achieve the above object, there is provided a method for driving a discharge device which has at least a pair of electrodes and generates a discharge by applying a discharge address pulse and a discharge sustaining pulse to at least one of the pair of electrodes, the driving method comprises the step of applying a space charge controlling pulse to at least one of the electrodes during a sustaining period.
Preferably, the space charge controlling pulse is applied during a pause period of the discharge sustaining pulse, the voltage level of the space charge controlling pulse is in a range in which a self-sustained discharge caused by the voltage itself is avoided, and the pulse width of the space charge controlling pulse is between 200 nsec-1 xcexcsec.
In the present invention, preferably, the discharge device comprises: a pair of electrodes in parallel for generating a sustainment discharge by alternately applying discharge sustaining pulses of the same polarity; and a third electrode orthogonal to the pair of electrodes, for generating an address discharge in cooperation with at least one of the pair of electrodes upon application of a discharge address pulse. Preferably, the space charge controlling pulse is applied to the third electrode during the pause period of the discharge sustaining pulse, or to at least one of the pair of parallel electrodes during the pause period of the discharge sustaining pulse, or to the pair of parallel electrodes and the third electrode. It is preferable that the space charge controlling pulse has a polarity which is the same as or opposite to that of the discharge sustaining pulse.
Also, preferably, the method for driving the discharge device in which the pair of parallel electrodes are covered with an insulation layer and the polarity of the discharge sustaining pulse varies with time, comprises the steps of: addressing a discharge by applying the discharge address pulse to the third electrode and thus selecting an intended pixel; and sustaining the discharge by applying the discharge sustaining pulse to at least one of the pair of parallel electrodes and thus maintaining luminescence of the selected pixel, wherein the discharge addressing step is temporally independent of the discharge sustaining step, and the discharge sustaining period includes repeated discharge sustaining pulses and discharge pause periods.
Also, preferably, the discharge device has a pair of parallel electrodes for generating a sustainment discharge by alternately applying discharge sustaining pulses of the same polarity. Preferably, the space charge controlling pulse having the same polarity as or the opposite polarity to that of the discharge sustaining pulse voltage is applied to the other electrode immediately after the discharge sustaining pulse applied to one of the pair of electrodes is terminated. Also, in the present invention, preferably, the discharge device has a pair of electrodes, to one of which a positive discharge sustaining pulse is applied and to the other of which a negative discharge sustaining pulse is applied. Preferably, the method for driving the drive device comprises the steps of: addressing a discharge by applying the discharge address pulse to at least one electrode of the paired electrodes and thus selecting an intended pixel; and sustaining the discharge by applying the discharge sustaining pulse to at least one of the pair of crossing electrodes and thus displaying the selected pixel luminescently, wherein the discharge addressing step is temporally independent of the discharge sustaining step, and the discharge sustaining period includes repeated discharge sustaining pulses and discharge pause periods.
Also, in the method for driving the discharge device of the present invention, preferably, a discharge sustaining pulse is applied only to one electrode of the pair of electrodes. Here, the discharge sustaining pulse has positive and negative polarities, alternately, and the space charge controlling pulse having a polarity opposite to that of the discharge sustaining pulse is applied to the other electrode immediately after the discharge sustaining pulse is applied. Also, as an alternative, one of the pair of electrodes is at 0V, the discharge sustaining pulse having positive and negative polarities is applied to the other electrode, and the space charge controlling pulse having the same polarity as that of the discharge sustaining pulse is applied after the discharge sustaining pulse.